Nitrate concentrations have increased in many Upper Floridian aquifer springs since the 1950s, exceeding 1 mg/L in recent years at some springs. The Upper Floridian aquifer is particularly vulnerable to impacts from anthropogenic activities in areas where the aquifer is not confined or only thinly confined, such as throughout much of Marion County, north-central Florida. Phelps (2004) reported that nitrate concentrations ranged from less than 0.02 to 12 mg/L, with a median of 1.2 mg/L, for 56 Upper Floridian aquifer wells sampled in Marion County during 2000-2001.
Stormwater runoff is one of the possible sources of nitrate, among others such as septic tanks, land-based application of reclaimed stormwater, or fertilizer, which can contribute to elevated nitrate concentrations in the Upper Floridian aquifer. As a Statewide unified rule for stormwater is developed, there is a need to quantify the effects of stormwater retention/detention ponds on the underlying aquifers. In general little research is available for a quantitative process-based understanding of the effects of sorption media that can be used in the field for nutrient removal.
As of March 2007, there were approximately 1250 water body segments on the State of Florida impaired water bodies list Florida Department of Environmental Protection, 2007. Of these waters, there are about 60% classified as either lakes or streams. About 45% of the lakes and streams are impaired as measured by nutrients. The Florida Department of Environmental Protection also published a comprehensive integrated assessment of water quality (Florida Department of Environmental Protection, 2006). This publication noted that for many of the springs in the State, the nitrate level increased by two to three times over the past 20 years. It is also known that nitrate concentrations have increased in many Floridian aquifer springs since the 1950s, exceeding 1 mg/L in recent years at some springs. The use of differing sorption media in wet and dry ponds turns out to be an appealing engineering approach in dealing with the increasing trend of higher nitrate concentrations that is expected to continue in the surface and groundwater systems.
The control of stormwater runoff is a pressing issue facing most urban areas where land availability for stormwater ponds is either not physically available or other stormwater options are very expensive. Stormwater runoff into separate or combined sewers can be polluted in several ways such as contact with corroded and deposited roof materials and contact with fecal matter, fertilizers and pesticides from lawns and agricultural land. One possible solution for treatment of roof runoff stormwater is the use of a green roof stormwater treatment and reuse system, which includes a cistern or holding pond from which stormwater is returned to the green roof, and less stormwater is discharged to receiving waters.
The most practical approach to the problem of stormwater runoff is to treat the stormwater as close to where it was contaminated as possible. The practice of using plant- and soil-based techniques for treating and holding stormwater at the source to decrease stormwater runoff and increase evapotranspiration rates is called low-impact development (LID). A completed water budget on a non-irrigated green roof and found that for small precipitation events, the green roof was able to retain approximately 75% of the precipitation and reduce the peak flow by as much as 90% as well as increase the time of concentration to almost four hours. The time of concentration is the amount of time it takes for stormwater runoff to occur after a precipitation event has begun.
As a Statewide unified rule for stormwater management is being developed in Florida, there is a need to combine field and laboratory data for designing effective passive in-situ treatment units within stormwater retention/detention ponds for ultimate control of nitrogen impact on groundwater in Florida. The current study examined the ability of different sorption media to sorb nitrogen from stormwater contaminated with various nitrogen fertilizers. Sorption media of interest include but are not limited to tire crumb, sawdust, activated carbon, iron amended resins, orange peel, peat, leaf compost, naturally occurring sands, zeolites, coconut husks, polymers, and soybean hulls. The study consisted of running both batch and packed bed column tests to determine the sorption capacity, the required sorption equilibration tire and the flow-through utilization efficiency of various sorption media under various contact times when exposed to stormwater contaminated with various nitrogen fertilizers.